Photographic printing apparatus

ABSTRACT

The need for a manual adjustment to the exposure to be made by a photographic printer having average and point-by-point density determining apparatuses is obviated by a device for selecting a principal subject area of a negative from which said point-bypoint density data is derived.

United States Patent King et al. [45] July 18, 1972 PHOTOGRAPHICPRINTING References APPARATUS UNITED STATES PATENTS [72] Inventors:James L. King, Rochest r; L 0, Am 2,444,675 7/1948 Rath ..356/203 XHamlin, both f v 5,480,424 8/ 192g gimmom. ,480,363 l1 l9 tewan... 8[73] Assignee: Eastman Kodak Company, Rochester, Primary Examiner-SamuelS. Matthews Assistant Examiner-Richard L. Moses [22] filed 1970Attorney-Walter o. Hodsdon and Robert F. Cody 21 Appl. No.: 66,299 [57]ABSTRACT The need for a manual adjustment to the exposure to be made bya photographic printer having average and point-by-point 152] US. Cl..355/83, 355/68 density determining apparatuses is obviated by a devicefor {g 2 2 selecting a principal subject area of a negative from whichsaid e o are L l/VE COUA/ 7' point-by-point density data is derived.

9 Claims, 4 Drawing Figures EXPOSURE COR/PEG T/UN COMPUTOR PHOTOGRAPHICPRINTING APPARATUS BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates in general to photographic printing apparatus;and more particularly, to an improved exposure control system for use ina photographic printer.

2. Description Relative to the Prior Art FIG. 1, which is a blockdiagram of a prior art exposure control system for a photographicprinter, and

FIG. 2, which is a block diagram of a computer system for use with theexposure control system of FIG. 1, are presented for the purpose ofevidencing a problem inherent in the use of prior art photographicprinters:

FIG. 3, which is a block diagram illustrating broadly an improvedsecondary exposure control system according to the invention, and FIG.4, which is a logical block diagram illustrating a schematic arrangementof one embodiment of the invention.

As indicated in FIG. I, the prior art exposure control system, overwhich apparatus according to the invention is an improvement,,hasprimary and secondary exposure control sections. Primary exposurecontrol of a photographic printer which control, incidentally, isadequate usually for about 80 percent of the negatives handled by aprinter is derived as follows: A light source illuminates a negative 12to be printed; and spatially disposed light which is transmitted throughthe whole negative is collected (14) and directed to a photodetectorcircuit 16. (Although the photodetector circuit 16 is shown as a singleblock in FIG. 1, it will be appreciated that, in color printing, thecircuit 16 will have three sections, respectively for the red, green,and blue color components of the negative 12.) Prior to adoption of theindicated secondary exposure control system of FIG. 1, it had been thepractice for an operator to modify the primary exposure control based ona visual analysis of the negative: The operator would examine thenegative to be printed (via a viewing gate) to determine whether theneutral density of the principal subject of the negative was similar tothe neutral density of the whole of the negative; and if such was notthe case, the printing (red, green, and blue) exposures would be,increased or decreased accordingly, viz.'by aselected one of severalamounts. (Typically, the operator would choose one of nine or tendiscrete manual corrections.) This procedure was time consuming andoften resulted in comparatively low yields of satisfactory prints, sincetheoperator was required to make difficult relative neutral densityjudgments. Furthermore, the probability that two operators wouldsimilarly judge a negative, or that the same operator wouldsimilarlyjudge a negative for a first and second printing of such negative, wasless than would otherwise be desired.

To overcome the inherent shortcomings of the primary, i.e. large areatransmittance exposure control of a printer, the secondary or subjectcorrection exposure control section of FIG. 1 was implemented: Ascanning device 18 makes a pointby-point neutral density examination ofthe negative to be printed and applies such density data via aphotodetector circuit 20 to an exposure correction computer 22, theoutput of which is summed (23) with the large area density output(s) ofthe circuit 16 to produce control signals for the (red, green, and blue)exposure controls of a printer.

The computer 22 works as follows: See FIG. 2.

The average neutral density A" of the negative is calculated by applyingthe scan signal D to an integrator 24; the sign of the signal A from theintegrator 24 is inverted (26) for a reason which will be apparentbelow. A signal X representing the peak (maximum) density which isdetected while scanning the negative is produced by a detector 28(adapted to receive thesignal D. And a contrast signal A is producedform the signal D by a circuit 30. The circuit 30 includes adifferentiator 32 which produces signals representing the rate of changeof density while scanning the negative; and an integrator 34 integratesthe absolute value of such difi'erential signals to produce the signal AThe signals A, X, and A are then algebraically summed (36) to produce asubject correction exposure control correction signal F.

Justification for making the subject correction F proportional to X maybe appreciated as follows: A relatively small, high density area (e.g.the face of a principal subject) in an otherwise low density negativewill be virtually ignored in an exposure control system predicatedsolely on the large area transmittance (or density) of the entirenegative. Hence, the corresponding area in the resulting photographicprint will tend to be excessively light or underexposed.

Justification for making the subject correction F proportional to -A"may be appreciated as follows: For a negative of essentially constantneutral density (A zero), the correction term F should be zero, and suchwill be the case when the signal A is equal to and opposite in sign tothe signal X.

Justification for making the subject correction F proportional to theaverage rate of density change A may be appreciated as follows:Negatives obtained from original scenes having abnormally high lightingratios (highlight to shadow) typically result in underexposed printswhen exposure control is predicated solely on large area transmittance.Hence, the rate of density change function A is used to increase thecorrection F for negatives of relatively high macro-contrast. For

negatives obtained from-flat" lighting situations, A is low andproportionately less exposure is obtained as a result of the influenceof the A signal on the exposure correction term F.

It is important to appreciate that the prior art of basing the subjectcorrection term F on functions of the scanned density D assumes thatthese statistical functions have typical relationships to the subjectmatter as indicated previously. However, when this assumption isinvalid, the correction term F will fail to produce a print ofsatisfactory density. For example, if the maximum density X obtainedfrom a point-by-point scan of the entire negative area is related tosome unusually bright object in the scene (windows, skies, etc.) ratherthan being representative of the principal subject density, thecorrection term F will not produce the desired exposure levels. Hence,the printer operator must be trained to recognize these unusual densityrelationships in negatives and to employ an operator-actuated override38 (not shown in FIG. 2). After visually comparing the neutral densityof the principal subject with other dark" areas in the negative, theoperator must decide whether these non-subject areas will producemisleading scan density information, e. g. -a scene in which the subject(typically a person) is backlighted and photographed against a bright.sky will yield X signals which are much too high to represent thedensity of the principal subject. To compensate for this violation ofthe underlying assumptions of the secondary exposure control system, theoperator actuates switch 40 to its INC" or DEC contacts; this actioncauses the exposure correction computer 22 to increase or decrease theexposure(s) as required. While such techniques reduce the number ofexposure correction choices which an operator has to make (viz., one ofthree choices rather than one of ten), the difficulties of makingsubjective judgments regarding relative densities of subject matter andthe attendant effects on print quality and printing production rates arestill evident in the prior art.

SUMMARY OF THE INVENTION The present invention is predicated on the factthat, while it may be difficult to tell whether the neutral density ofthe principal subject of a photographic negative is more or less than,or the same as, the neutral density of other areas of the negative, thelocation of such principal subject within such negative is acomparatively easy thing to do. And thus the invention proposes, in aphotographic exposure control system of the type having a primary (largearea) exposure control, and a scanning-type secondary exposure controlcooperative with the primary control, that scan density data employedfor purposes of exposure correction be derived (principally) from thatarea of a negative containing the principal subject.

OBJECT OF THE INVENTION To provide, for a photographic printer, animproved exposure control system, whereby printing production rates maybe increased, and printing operations may be simplified.

FIG. 3 indicates apparatus similar to the subject correction exposurecontrol system of FIG. 1 (S-S), save for the sub stitution of an areaselector 42 for the exposure increase or decrease override 38 of FIG. 1.Corresponding parts of the two figures are similarly numbered. Theselector 42, when actuated by an operator, effectively picks the area ofa negative from which subject correction exposure control data is to bederived; and since data corresponding to the selected area is the onlydata applied to, and operated upon by, the exposure correctioncomputer.22, the resultant scan density functions inherently do notcontain misleading information from the rest of the negative. The scanarea selector 42 may take a variety of forms: For example, the scan areaselector may take the form of a computer adapted to determineautomatically the principal subject area of a negative, and in responseto such determination to correct primary exposure control in accordancewith data corresponding to such computed area;

or it may take the form of a device that uses scan data from all of anegative, but weights the significance of such data in accordance withan operator-determined area selection, etc.

Reference should now be made to F 1G. 4 for the details of a subjectcorrection exposure control based on a negative scanning system that hasbeen modified to accommodate the invention: The negative 12 from which aprint is to be made is illuminated by a light source 10. Lighttransmitted through the negative 12 is directed to a primary exposurecontrol system (see FIG. 1), to a negative scanning system 44, and to anegative viewing station 46.

The scanning system comprises a rotatable drum 48 having a mirror 50'disposed therein. Means for rotating the drum 48 may take any of avariety of forms. The image of the negative 12 is projected by means ofa lens 50 and a mirror 50' to the inside surface 52 of the rim 54 of thedrum 48; and the rim 54 is provided with helically disposed apertures 56which, when the drum 48 rotates, successively scan across respectivelines of the negative image. Light, therefore, is transmitted throughthe apertures 56 in proportion to the point-by-point optical density ofthe negative 12. A lens 58 focuses the light output from the apertures56 to a photocell 60; and such photocell 60 applies its densitydependent output signals to an AND circuit 62.

A timing disk 64, which is rotated in unison with the drum 48, has, inthis embodiment of the invention, three staggered apertures 66 for eachscanning aperture 56 which appears in the rim 54 of the drum 48. Thedisk 64 is illuminated by a light source; and radially (with respect tothe disk) aligned photocells 68 receive light from their respectiveapertures 68 successively as the timing disk rotates. (See the waveformoutputs from the photocells 68,

At the start of each scan line, the photocell 68 pulses a counter 70which is adapted to reset itself after each full rotation of thescanning drum, i.e. after the negative image 52 has been scannedcompletely. To assure that the count in the counter 70 is alwaysproperly representative of a respective scan of the negative image 52, atiming aperture 72 is provided in the disk 64; and such aperture 72cooperates with a photocell 74 (radially aligned like the photocells 68,to reset the counter at the start of each rotation of the drum 48. Adecoder 76 cooperates with the counter 70 to excite one of its threeoutput leads depending on whether the count of the counter 70 is betweenzero and Y, between Y and 2Y, or between 2Y and 3Y; and such decoder,like the photocells 68, cooperates with a keyboard 42 in a manner to bedescribed momentarily. The keyboard 42' which may take any of a varietyof forms is of the type which, when a key is pressed,'all other keys areeffectively released.

The negative 12 may be viewed directly, or indirectly by means of ascreen 78 as shown. In either event, however, it is desirable to employa reticle 80 for optically sub dividing the negative into severalsmaller areas (nine equisized areas in this embodiment).

Assume the principal subject of the negative resides within the comer ofthe negative 12 which corresponds with the keyboard location 1: Theprinter operator, on seeing this, and ignoring matters of neutraldensity comparisons, presses key number 1"; and for the first third ofeach scan line, a circuit cooperative with key number 1 is actuated.That is, simultaneously occurring signals Y L, cause an AND gate 82 toapply an output signal via the key-operated switch 1 to an OR circuit86. The OR circuit 86 in turn applies its output to the AND circuit 62so that such AND circuit 62 can apply scan density signals to theexposure correction computer 22 for the time that the scanning drum 48is examining the area 1 of the negative. Similarly, if the principalsubject of the negative had occupied, say negative area 8, second third(L of each scan line within the last third (Y of all such lines, keynumber 8 would have been pressed by the operator, etc.

Whereas apparatus according to the prior art produces neutral densityscan data signals from the whole of a negative, which data has to besubjectively monitored by an operator, to correct primary exposurecontrol within a printer, apparatus according to the invention obviatessuch subjective monitoring by the use of scan data derived from aselected area of a negative containing the principal subject of suchnegative.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention. For example, it is within the purview of the invention toemploy for most negatives a normally-engaged scan selector that limitsnegative scanning to the production of scan data signals that correspondwith a centrally disposed negative area (see FIG. 4); and to employ akeyboard selector solely for the purpose of zeroing in on a selectednegative area.

What is claimed is: v 1 I. In a photographic printer having:

a. control means for regulating the exposure of print material, and b.means responsive to the density characteristics of the means to beprinted for controlling the operation of said control means, saidresponsive means comprising:

1. means for producing a signal proportional to the average density ofsaid means to be printed,

2. means for scanning said means to be printed and producing signalsrepresentative of the point-by-point density characteristics of at leastsome area of said means to be printed,

3. means adapted to receive said signals from said scanning means forproducing a correction signal, and

4. means for combining said average density signal and said correctionsignal into a resultant signal, said resultant signal being applied tosaid control means for regulating said exposure of said print material,

the improvement of means cooperative with said responsive means forproducing signals corresponding to a set of pointby-point densitycharacteristics for respective areas within said area of said means tobe printed, and means for weighting the different point-by-point densitycharacteristics within said set thereof according to the respectiveareas of said means to be printed, thereby to produce a correctionsignal for said average density signal.

2. In a photographic printer having:

a. control means for regulating the exposure of print materia l, and

b. means responsive to the density characteristics of the means to beprinted for controlling the operation of said control means,

said responsive means comprising:

1. means for producing a signal proportional to the average density ofsaid means to be printed,

2. means for scanning said means to be printed and producing signalsrepresentative of the point-by-point density characteristics of at leastsome area of said means to be printed,

3 means adapted to receive said signals from said scanning means forproducing a correction signal, and 4. means for combining said averagedensity signal and said correction signal into a resultant signal, saidresultant signal being applied to said control means for regulating saidexposure of said print material, the improvement of means cooperativewith said responsive means for selecting an area from within said areaof said means to be printed form which said correction signal shall bepredominantly dependent, said means for selecting comprising a pluralityof switch means, each of which corresponds to a respective area of themeans to be printed.

3. The improvement of claim 2 including a reticle for defining therespective areas of the said means to be printed.

4. The improvement of claim 2 wherein said switch means are arranged inthe form of a keyboard, the respective keys of which are positioned onsaid keyboard to correspond positionwise with respective areas of andwithin said means to be printed.

5. Apparatus for use with a photographic printer comprising:

a. means for scanning a negative from which a print is to be made toproduce signals representative of the point-bypoint optical density ofsaid negative,

b. means for selecting from all said density signals those signals whichcorrespond to a selected area of interest within said negative,

c. means adapted to receive said selected signals for computingtherefrom a control signal, and

d. means responsive to said control signal for regulating in accordancetherewith the exposure of said printer.

6. The apparatus of claim 5 wherein said selecting means comprises akeyboard, and respective switch means cooperative with the keys of saidkeyboard, said switch means being respectively adapted to apply selectedsignals from among said density signals to said exposure regulatingmeans.

7. The apparatus of claim 6 wherein said keyboard has an area formatsubstantially like the area format of a negative to be printed by saidprinter, and wherein each of said switch means cooperative with the saidkeys is adapted to apply to said exposure regulating means densitysignals respectively corresponding to a respective area within saidnegative.

8. The apparatus of claim 7 including reticle means cooperative withsaid negative to subdivide said negative into areas corresponding to thearrangement of keys on said keyboard.

9. In a photographic printer,

a. means for scanning line-by-line a means to be printed and producingtherefrom signals representing the point-bypoint optical density of saidmeans to be printed,

b. means for dividing the signals from each of said scan lines intoline-segment groups of signals,

c. means for grouping the signals from said scan lines into sets ofsignals,

d. means for selecting signals which simultaneously obtain in a givenset and a given group of signals, and

e. means responsive to the selected signals for controlling the printingexposure of said printer.

1. In a photographic printer having: a. control means for regulating theexposure of print material, and b. means responsive to the densitycharacteristics of the means to be printed for controlling the operationof said control means, said responsive means comprising:
 1. means forproducing a signal proportional to the average density of said means tobe printed,
 2. means for scanning said means to be printed and producingsignals representative of the point-by-point density characteristics ofat least some area of said means to be printed,
 3. means adapted toreceive said signals from said scanning means for producing a correctionsignal, and
 4. means for combining said average density signal and saidcorrection signal into a resultant signal, said resultant signal beingapplied to said control means for regulating said exposure of said printmaterial, the improvement of means cooperative with said responsivemeans for producing signals corresponding to a set of point-by-pointdensity characteristics for respective areas within said area of saidmeans to be printed, and means for weighting the differentpoint-by-point density characteristics within said set thereof accordingto the respective areas of said means to be printed, thereby to producea correction signal for said average density signal.
 2. means forscanning said means to be printed and producing signals representativeof the point-by-point density characteristics of at least some area ofsaid means to be printed,
 2. In a photographic printer having: a.control means for regulating the exposure of print material, and b.means responsive to the density characteristics of the means to beprinted for controlling the operation of said control means, saidresponsive means comprising:
 2. means for scanning said means to beprinted and producing signals representative of the point-by-pointdensity characteristics of at least some area of said means to beprinted, 3 means adapted to receive said signals from said scanningmeans for producing a correction signal, and
 3. means adapted to receivesaid signals from said scanning means for producing a correction signal,and
 3. The improvement of claim 2 including a reticle for defining therespective areas of the said means to be printed.
 4. The improvement ofclaim 2 wherein said switch means are arranged in the form of akeyboard, the respective keys of which are positioned on said keyboardto correspond positionwise with respective areas of and within saidmeans to be printed.
 4. means for combining said average density signaland said correction signal into a resultant signal, said resultantsignal being applied to said control means for regulating said exposureof said print material, the improvement of means cooperative with saidresponsive means for producing signals corresponding to a set ofpoint-by-point density characteristics for respective areas within saidarea of said means to be printed, and means for weighting the differentpoint-by-point density characteristics within said set thereof accordingto the respective areas of said means to be printed, thereby to producea correction signal for said average density signal.
 4. means forcombining said average density signal and said correction signal into aresultant signal, said resultant signal being applied to said controlmeans for regulating said exposure of said print material, theimprovement of means cooperative with said responsive means forselecting an area from within said area of said means to be printed formwhich said correction signal shall be predominantly dependent, saidmeans for selecting comprising a plurality of switch means, each ofwhich corresponds to a respective area of the means to be printed. 5.Apparatus for use with a photographic printer comprising: a. means forscanning a negative from which a print is to be made to produce signalsrepresentative of the point-by-point optical density of said negative,b. means for selecting from all said density signals those signals whichcorrespond to a selected area of interest within said negative, c. meansadapted to receive said selected signals for computing therefrom acontrol signal, and d. means reSponsive to said control signal forregulating in accordance therewith the exposure of said printer.
 6. Theapparatus of claim 5 wherein said selecting means comprises a keyboard,and respective switch means cooperative with the keys of said keyboard,said switch means being respectively adapted to apply selected signalsfrom among said density signals to said exposure regulating means. 7.The apparatus of claim 6 wherein said keyboard has an area formatsubstantially like the area format of a negative to be printed by saidprinter, and wherein each of said switch means cooperative with the saidkeys is adapted to apply to said exposure regulating means densitysignals respectively corresponding to a respective area within saidnegative.
 8. The apparatus of claim 7 including reticle meanscooperative with said negative to subdivide said negative into areascorresponding to the arrangement of keys on said keyboard.
 9. In aphotographic printer, a. means for scanning line-by-line a means to beprinted and producing therefrom signals representing the point-by-pointoptical density of said means to be printed, b. means for dividing thesignals from each of said scan lines into line-segment groups ofsignals, c. means for grouping the signals from said scan lines intosets of signals, d. means for selecting signals which simultaneouslyobtain in a given set and a given group of signals, and e. meansresponsive to the selected signals for controlling the printing exposureof said printer.